1. Field of the Invention.
This invention relates to processes for producing reinforced plastic articles, and more particularly, to processes for pultruding fiber reinforced thermoplastic articles.
2. 2. Description of the Prior Art.
Processes for producing fiber reinforced plastic articles by the technique of pultrusion are well known. In such a process, prepreg feed material comprising a plurality of reinforcing fiber strands surrounded by a resin matrix is pulled through a heated forming die. Common types of articles produced by pultrusion processes include channels, rods, bars and slats. Although pultrusion processes were limited to the use of thermoset resins at one time, pultrusion processes for forming reinforced plastic articles from thermoplastic resins have now been developed.
Most pultrusion processes can be characterized as either wet or dry. In a wet pultrusion process, a plurality of fiber strands are pulled from a creel and through a resin bath for impregnation of the strands with the resin. Typically, excess resin is then removed from the strands. The resin impregnated fiber strands, now referred to as "prepreg feed material", are then pulled through a heated forming die and cooled to form a plastic composite or article of a continuous length. The article is typically cut into long portions which are either stored or transported elsewhere for further processing.
Dry pultrusion processes do not include the step of passing a plurality of fiber strands through a resin bath and the other steps associated with initially forming the resin impregnated fiber strands or prepreg feed material. In a dry pultrusion process, the prepreg feed material fed into the heated forming die is pre-impregnated material formed in a separate process. Such pre-impregnated material can be, for example, unidirectional tape or fabric prepreg. As in wet pultrusion processes, the prepreg feed material is pulled through a heated forming die and cooled to form an article of continuous length.
By the present invention, it has been discovered that a previously pultruded article having a substantially different shape than the final product can be employed as the prepreg feed material fed into the heated forming die in a dry pultrusion process. As long as it has approximately the same longitudinal cross-sectional area or volume, the prepreg feed material can have any longitudinal cross-sectional configuration. In this way, previously pultruded articles such as rods can be re-pultruded into different articles such as bars or various types of beams. This expands the utility of pultrusion processes in general and expands the utility of the articles produced thereby.